The invention relates to an improved star disk for an electrically-excited electric machine.
In electrically-excited electric machines, star disks are used for the mechanical support of the end windings of the rotor in response to high centrifugal forces associated with the rapid rotation of the rotor. Star disks can prevent a defect of the electric machine associated with a failure of a winding in the end winding area. Star disks are fitted to the axial end of the rotor. One side of the star disk adjoins the laminate stack of the rotor, and may be electrically isolated from the latter. The rotor windings are routed on the other side of the star disk. At their radial end, star disks from the prior art are customarily provided with a projection, by means of which the rotor accommodates the centrifugal forces of the end windings. It is understood that the projection is subject to high mechanical loading as a result.
Electrically-excited machines also pose a problem, in that heat losses occurring within the rotor need to be evacuated. In the prior art, in some cases, cooling ducts are provided in the rotor, through which a coolant fluid flows. Firstly, these arrangements are expensive, and secondly they cannot ensure the cooling of the end windings to the requisite degree.
Accordingly, the object of the invention is to provide an improved star disk with better mechanical support for the end windings and/or which cools the end windings more effectively.
This and other objects a achieved by a rotor element and an electric machine having such a rotor element, in accordance with embodiments of the invention.
A rotor element according to the invention is designed to be arranged on an electrically-excited rotor of an electric machine. The rotor element comprises a base which is designed to be arranged in the insert between the axial end of a laminate stack of the rotor and at least one end winding. The rotor element comprises at least one fin, which is fastened on the base and is designed to protrude in the insert through at least one end winding axially out of the at least one end winding.
The rotor element may be a “star disk”. As at least one fin runs from the base of the rotor element through the end winding, the mechanical stability of the rotor, and specifically the mechanical stability of the winding, is improved. This is because the winding is mechanically supported at a number of points. Moreover, the fin can conduct heat from the interior of the end winding to the exterior, thereby improving the cooling of the end winding.
On an outer radial area of the rotor element, an end element may be arranged, which extends axially into the insert, and is designed to be arranged in the insert radially outwards from the end winding. The end element mechanically supports the radial outer end of the end winding.
The at least one fin may terminate within the end winding or at the outer edge of the end winding, and thus primarily fulfils a mechanical support function. Preferably, however, the fin also projects beyond the end winding, and thus additionally fulfils a cooling function. The at least one fin projects beyond the end winding by preferably 100%, more preferably by 150%, and most preferably by at least 200% of the thickness of the end winding. Heat from the end winding is conducted by the fins and dissipated in the motor interior. The further the fin projects from the rotor winding, the more heat can be dissipated. However, a greater fin length will increase space requirements in the axial direction.
On the side facing the end windings, the rotor element may be configured convexly. The end windings are thus protected against damage from the rotor element.
On the side facing the laminate stack, the rotor element may be configured for electrical isolation. By this arrangement, an electrical short-circuit on the laminate stack is prevented. Naturally, the rotor element is not necessarily required to touch the laminate stack, and any other elements may be arranged between the rotor element and the laminate stack.
The rotor element may be formed of metal, aluminum and/or of a plastic material. For example, the fin of the rotor element may be constructed of metal, in order to ensure optimum thermal conduction. The laminate stack-facing side of the rotor element may be constructed of a plastic material, in order to ensure good insulating properties.
The object of the invention is fulfilled by an electric machine with a stator and a rotor, which rotor is arranged within the stator. The stator and the rotor may be provided with windings which generate a magnetic field when current flows therein. The above-mentioned rotor element may be arranged at an axial end of the rotor, whereby the rotor element is not necessarily in contact with the rotor, and any other elements may be arranged between the rotor element and the rotor. For example, the rotor element may be in contact with the laminate stack of the rotor. At least one end winding of the rotor winding may be arranged above the base of the rotor element. The electric machine may be a motor and/or a generator. The rotor element protects the rotor winding against mechanical damage by centrifugal forces, and conducts thermal losses away from the end winding.
The electric machine may be provided with a stator fin, which is adjacent to the fin on the rotor element. The stator fin may be configured in a fixed arrangement in relation to the stator of the electric machine. The stator fin can receive thermal radiation and/or convective heat which is emitted from the fin. The stator fin can dissipate the heat thus captured, for example to an end housing of the electric machine. From here, heat is dissipated into the vehicle cooling system.
The stator fin may project between two fins on the rotor element and/or between one fin and the end element of the rotor element. The electric machine may be provided with a stator fin arrangement comprised of at least two stator fins, whereby one fin on the rotor element projects between two stator fins. By these arrangements, the transmission of heat from the end windings to the stator fins is improved.
The fins on the rotor element may be arranged concentrically to the axis of rotation. The fins may also be used for the balancing of the rotor. Using the star disk according to the invention, the end windings of the rotor are fanned out by a star disk with integral fins. Accordingly, mechanical loads on the end windings of the rotor are fanned out over a number of points. Consequently, the cooling of the end windings is improved by the shorter thermal conduction paths. Stator fins may be arranged in the end housing of the rotor, in order to improve heat transfer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.